I cant see any real difference between photoautotrophs and photoheterotrophs, if im not mistakin they both obtain carbon from there invirment and recieve energy from the sun. I do know that the former uses Co2 and the latter uses other carbon based compounds but this difference seems mundane to me

Photoautotrophs: Bacteria that use sunlight as their energy source and carbon dioxide (as part of photosynthesis) as their carbon source. These bacteria thus obtain all their nourishment through photosynthesis

Photoheterotrophs: Bacteria that use sunlight as their energy source and organic compounds from the environment as their carbon source.

There are basically 4 different types of metabolism: Photoautotrophs, Photoheterotrophs, Chemoautotrophs, chemoheterotrophs.Both types of phototrophs use light as their energy source ( as opposed to Chemotrophs which use oxidation as their energy source).Photoautotrophs fix inorganic carbon from carbon dioxide into organic carbon in the presence of water. (for example plants). They also produce oxygen as a by product.Photoheterotrophs need organic carbon, so they need the carbon produced by plants or other organisms for their nutrients.So photoautotrophs form the basis of the food chain and basically keep the world running.

Mixotrophic is when an organism is both autotrophic and heterotrophic.